Down-regulating a fiber-specific KCR like gene GhKCRL1 suppressed fiber elongation through blocking the synthesis of sphingolipids in fiber cell

Cotton is an important natural fiber crop in the world. Cotton fiber cell is an extremely elongated single-cell trichome of seeds. Therefore, the fiber cell is an ideal model for studying plant cell elongation (polar expansion) and secondary wall deposition. Moreover, the two processes determine the quality (length, strength and fineness) of mature cotton fiber. However, the regulatory mechanism of fiber elongation remains unclear. Ligon lintless-1 ( Li-1 ) mutant is a fiber elongation mutant and a good material to study fiber elongation. In the present study, through analyzing the different expression genes in 10-DPA (day post anthesis) fiber cell of Li-1 mutant and its wild type (TM-1), we found a KCR (3-Ketoacyl-Coenzyme A Reductase) like gene, GhKCRL1 , was strikingly down-regulated in Li-1 mutant. GhKCRL1 shared low sequence identity with the 17 beta-hydroxysteroid dehydrogenase 12 of animal and the reported GhKCR1, GhKCR2, and GhKCR3 of upland cotton. GhKCRL1 was specifically expressed in fiber cells and its expression level peaked in 10-DPA fiber cells. GhKCRL1 is located in the endoplasmic reticulum . Down-regulating the expression of GhKCRL1 suppressed fiber elongation and significantly shortened mature fiber length. The sphingolipids contained VLCFA and LCFA strikingly declined in RNAi fiber cells. Consistently, the expression levels of most genes involved in sphingolipid biosynthesis and very long chain fatty acid (VLCFA) biosynthesis decreased in GhKCRL1 down-regulated cotton fibers. And the exogenous application of VLCFA (C24 FA) could rescue the elongation of GhKCRL1 down-regulated fiber cells. Taken together, the results revealed that the fiber-specific GhKCRL1 play some roles in cotton fiber elongation by regulating sphingolipid biosynthesis. Pattern diagram of the GhKCRL regulating fiber elongation. • GhKCRL1 is a novel KCR gene in upland cotton. • GhKCRL1 specifically expressed in fibers cells. • Down-regulating GhKCRL1 expression suppressed fiber cell elongation. • Down-regulating GhKCRL1 blocking the synthesis of sphingolipids in fiber cell.